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21.
Effect of iron availability on expression of the Bradyrhizobium japonicum hemA gene. 总被引:3,自引:2,他引:1
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Bradyrhizobium japonicum produces delta-aminolevulinic acid, the universal precursor of tetrapyrroles, in a reaction catalyzed by the product of the hemA gene. Expression of the B. japonicum hemA gene is affected by iron availability. Activity of a hemA-lacZ fusion is increased approximately threefold by iron, and RNA analysis indicates that iron regulation is at the level of mRNA accumulation. To our knowledge, this is the first example of an iron-regulated heme biosynthetic gene in prokaryotes. 相似文献
22.
A. G. Connolly I. D. Godwin M. Cooper I. H. DeLacy 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(3-4):332-336
In this paper we present a method for the generation of randomly amplified polymorphic DNA (RAPD) markers for sweet potato. These were applied to produce genetic fingerprints of six clonal cultivars and to estimate genetic distances between these cultivars. The level of polymorphism within the species was extremely high. From the 36-decamer random primers used, 170 fragments were amplified, of which 132 (77.6%) were polymorphic. Ten primers resulted in no detected amplification. Of the remaining 26 primers for which amplification was achieved, only one did not reveal polymorphism. Six primers used alone enabled the discrimination of all six genotypes. Pattern analysis, which employed both a classification and ordination method, enabled the grouping of cultivars and the identification of primers which gave greatest discrimination among the cultivars. 相似文献
23.
Tyrosine kinase activity may be necessary but is not sufficient for c-erbB1-mediated tissue-specific tumorigenicity. 总被引:2,自引:2,他引:0
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![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Expression of mutant avian c-erbB1 genes results in tissue-specific transformation in chickens. Site-directed mutagenesis was used to generate kinase-defective mutants of several tissue-specific v-erbB transforming mutants by replacement of the ATP-binding lysine residue in the kinase domain with an arginine residue. These kinase-defective v-erbB mutants were analyzed for their in vitro and in vivo transforming potentials. Specifically, kinase-defective mutants of erythroleukemogenic, hemangioma-inducing, and sarcomagenic v-erbB genes were assessed for their oncogenic potential. In vitro transformation potential was assessed by soft-agar colony formation in primary cultures of chick embryo fibroblasts (CEF). In vivo transformation potential was determined by infection of 1-day-old line 0 chicks with concentrated recombinant retrovirus and then monitoring of birds for tumor formation. These transformation assays demonstrate that kinase activity is absolutely essential for transformation by tissue-specific transforming mutants of the avian c-erbB1 gene. Since all of the tissue-specific v-erbB mutants characterized to date exhibit tyrosine kinase activity in vitro but do not transform all tissues in which they are expressed, we conclude that v-erbB-associated tyrosine kinase activity may be necessary but is not sufficient to induce tumor formation. 相似文献
24.
Synthesis and properties of oligodeoxynucleotides containing the analogue 2'-deoxy-4'-thiothymidine. 总被引:1,自引:1,他引:0
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![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The 2'-deoxythymidine analogue 2'-deoxy-4'-thiothymidine has been incorporated, using standard methodology, into a series of dodecadeoxynucleotides containing the EcoRV restriction endonuclease recognition site (GATATC). The stability of these oligodeoxynucleotides and their ability to act as substrates for the restriction endonuclease and associated methylase have been compared with a normal unmodified oligodeoxynucleotide. No problems were encountered in the synthesis despite the presence of a potentially oxidisable sulfur atom in the sugar ring. The analogue had very little effect on the melting temperature of the self-complementary oligoeoxynucleotides so synthesised and all had a CD spectrum compatible with a B-DNA structure. The oligodeoxynucleotide containing one analogue in each strand within the recognition site, adjacent to the bond to be cleaved (i.e. GAXATC, where X is 2'-deoxy-4'-thiothymidine), was neither a substrate for the endonuclease nor was recognized by the associated methylase. When still within the recognition hexanucleotide but two further residues removed from the site of cleavage (i.e. GATAXC), the oligodeoxynucleotide was a poor substrate for both the endonuclease and methylase. Binding of the oligodeoxynucleotide to the endonuclease was unaffected but the kcat value was only 0.03% of the value obtained for the parent oligodeoxynucleotide. These results show that the incorporation of 2'-deoxy-4'-thionucleosides into synthetic oligodeoxynucleotides may shed light on subtle interactions between proteins and their normal substrates and may also show why 2'-deoxy-4'-thiothymidine itself is so toxic in cell culture. 相似文献
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OBJECTIVES--In an epidemic: to measure the incidence and risk of complications of influenza; to determine the effect of pre-existing disease on complications; to estimate vaccine uptake and efficacy. DESIGN--Case-control study. SETTING--Primary care: two group practices. SUBJECTS--342 of the 395 cases of clinically diagnosed influenza reported to the general practice surveillance of infectious diseases scheme of the Public Health Laboratory Service during the 1989 epidemic, and 342 age and sex matched controls. INTERVENTIONS--Examination of records. MAIN OUTCOME MEASURES--Documented recognised complications; hospital admission; previous vaccination. RESULTS--Of 15 recognised complications, bronchitis was the commonest (rate 190.1/1000 cases) and significantly commoner in cases (summary odds ratio 9.7) after adjusting for higher consultation rates (mean 6.1 per annum v 4.2 among controls; p < 0.0001). No deaths were recorded. The risk of bronchitis complicating influenza was higher in patients with pre-existing illnesses regarded as an indication for vaccination (odds ratio 3.3; p < 0.0001). Observed vaccination efficacy in those with pre-existing illnesses and in elderly subjects was high (63% and 77% respectively) but uptake was low (4.5% and 6.1% respectively). CONCLUSIONS--Bronchitis complicates about one fifth of all cases of influenza presenting to general practitioners. Patients with pre-existing illnesses regarded as an indication for vaccination are particularly at risk. Vaccine uptake is extremely low, precluding an unequivocal demonstration of a protective effect. 相似文献
27.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
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We examined variation in courtship activity and hormone levels of male and female wood ducks (Aix sponsa) in relation to hatch date. Young wood ducks were assigned in groups of 8 (4 males and 4 females) to 4 experimental pens; 2 pens contained early-hatched ducks (3-12 April) and 2 pens contained late-hatched ducks (7-16 June). Courtship behaviors occurred less frequently in October and November than in December and January-February for both early- and late-hatched groups. Early-hatched wood ducks participated in courtship more frequently and formed pair bonds sooner than late-hatched individuals. Testosterone (T) and androstenedione (AD) levels of males did not differ between treatment groups; however, average levels of luteinizing hormone (LH) were greater for early-hatched males. Differences in LH occurred in 2 of 12 samples (6 October and 3 November); otherwise, LH did not vary by treatment. Levels of T and LH in males varied temporally, but there was no significant temporal variation in AE levels. Temporal variation in hormone levels was similar for early- and late-hatched males. Estradiol (E), progesterone (P), and LH levels of females did not differ between treatment groups. There was temporal variation in levels of E and LH, but not of P; this variation was similar for early- and late-hatched females. These data indicate that behavioral differences occurring temporally and between early- and late-hatched wood ducks were not related to corresponding differences in hormone levels. 相似文献